Patent GB-606326-A (GB)
Title: Improvements in or relating to systems for supplying electric power to a load circuit
IPC: B23K11/26
Filed: 1946-03-05
Abstract: 606,326. Electricity supply. WESTING - HOUSE ELECTRIC INTERNATIONAL CO. March 5, 1946, No. 6816. Convention date, June 21, 1941. [Class 38 (iv)] A capacitor discharge type welding system having valve means of the arc discharge type for completing the discharge circuit of the capacitor is characterised by control means for preventing the discharge of the capacitor except when the voltage of the same is at or above a predetermined value. In Fig. 1, a condenser 17 is adapted to be charged from a D.C. source 18 and is subsequently discharged through the primary 16 of a welding transformer 12 to effect welding of a workpiece 14 between electrodes 15, 15. An arc discharge device 20 is rendered non-conductive by the application of a negative bias voltage to the control grid 28 of a gas discharge device 25 until the charge on the condenser 17 reaches its predetermined value. The negative bias is derived from the potentiometer 30 connected across the impedance 19 in the charging circuit for the condenser 17, such that as the voltage of the condenser builds up, the bias voltage decreases until the gas-discharge device 25 is rendered conductive to initiate conduction of the device 20. In the .arrangement of Fig. 2 (not shown), as applied to an induction heating furnace, a back-to-back arrangement of arc discharge devices is employed wherein an auxiliary condenser effects the passage of highfrequency current from the discharge circuit through their control electrodes to maintain the devices conductive alternately, subsequent to' initial ignition by a gas discharge such as device 25. Fig. 3 (not shown), shows a welding system in which back-to-back arc discharge devices in the discharge circuit of the main condenser are initially rendered conductive by a low-pressure gap device connected in parallel with the auxiliary condenser. In the arrangement of Fig. 4, for an induction heating furnace 36 the condenser 17 is charged from A.C. mains through an oxcillatory circuit including resistor 68 and inductance 69 and an oscillatory discharge is maintaned through a single arc discharge device 72 by means of a low-pressure gap device 60. Fig. 5 shows a welding system, wherein back-to-back arc discharge devices 20, 40 are rendered conductive only on odd spaced half-cycles of the condenser voltage wave. The condenser is charged from A.C. mains through an impedance 80 having an inductance of approximately one-half that of the condenser 17. In a modification, Fig. 7, periodic connection of the condenser 17 to an A.C. source 99 is controlled by additional back-to-back arc discharge devices in association with a synchronous timer 100 and phase-shifting means 116 determining the conduction of these discharge devices. In the arrangement of Fig. 8 (not shown), arc discharge devices are rendered conductive only for predetermined time intervals by means of a timing circuit controlling the application of the voltage of the main condenser to the control grids of the associated gas-discharge devices. In the arrangement of Fig. 9, alternative means for rendering gasdischarge devices 82, 83 selectively conductive in response to variations of voltage in the discharge circuit of the condenser 17, comprises' a resistance condenser network connected between the grids 88, 89 of the devices 82, 83' for applying bias voltages to the grids independently of the source. Fig. 12 (not shown), shows an arrangement incorporating an additional feature whereby it is ensured that the arc discharge devices of Fig. 9, are rendered non-conductive as soon as the voltage of the main condenser falls to the predetermined value, regardless of fixed bias voltage produced to render them conductive when the condenser voltage is at or above the predetermined value. Fig. 14 (also not shown), shows a  modified form of circuit embodying the invention as applied to an induction heating arrangement. The invention is also applicable to arcwelding.